Field of the Invention
The present invention relates to image forming apparatuses, such as a copier, a printer and a facsimile apparatus, which use electrophotographic and electrostatic recording schemes.
Description of the Related Art
Conventionally, image forming apparatuses that use the electrophotographic scheme and the like include an image forming apparatus of an intermediate transfer scheme where an image is output by secondarily transferring, onto a transfer material, a toner image having been transferred from an image bearing member onto an intermediate transfer member. An intermediate transfer belt that has an endless-belt shape is widely adopted as the intermediate transfer member. Each of primary transfer and secondary transfer is performed by applying a voltage to a transfer member disposed in contact with the intermediate transfer belt and by supplying transfer current in many cases. Transfer rollers (a primary transfer roller and a secondary transfer roller) which are roller-shaped transfer members are widely adopted as a primary transfer member and a secondary transfer member.
In such an image forming apparatus, the electric resistance value of the transfer roller tends to increase with increase in the amount of use of the transfer roller owing to the variation in the state of a conductive material and adhesion of dust, such as paper powder. When the electric resistance value increases to an acceptable range or more, a transfer failure due to shortage of transfer current sometimes occurs. Accordingly, when the life is set based on the index value of the amount of use, such as the printing sheet number or the total rotation time, and the index value reaches a value corresponding to the life, a transfer roller or a unit that includes the transfer roller is recommended to be replaced in some cases. However, the degree of increase in the electric resistance value of the transfer roller is different with the usage situations (the difference in the transfer members or the difference in output images) of the image forming apparatus. Consequently, when the life is uniformly determined based on the index value of the amount of use of the transfer roller, it is difficult to determine the life of the transfer roller correctly. Replacement of the transfer roller that has not reached the life yet in actuality sometimes causes unnecessary maintenance cost, and continuous use of the transfer roller having reached the life in actuality sometimes causes a transfer failure.
Japanese Patent Application Laid-Open No. 2003-195700 proposes that the electric resistance value of a transfer roller be measured, and if the electric resistance value is out of an acceptable range, it is determined that the life of the transfer roller or a unit that includes the transfer roller is reached.